Neutral-ionic transition in dimethyl-TTF-chloranil

We report on a new mixed-stack organic charge-transfer crystal of 2,6-dimethyltetrathiafulvalene-p-chloranil (DMTTF-CA), which undergoes a temperature-induced neutral-ionic transition (TINIT). The discontinuous change in molecular ionicity was found to occur at 65K. A most striking feature of the TINIT in DMTTF-CA was that a neutral-ionic coexisting phase appeared at lower temperatures, unlike the homogeneous ionic phase observed for the TINIT of TTF-CA. The pressure-induced transition in DMTTF-CA was found to occur at 1.2 GPa. The transition characteristics of DMTTF-CA are discussed in comparison with those of TTF-CA.